1. Field of the Invention
The present invention relates to anti-deflection tooling that reduces the deflection of a chuck when a workpiece is clamped in it.
2. Background Art
In the past few decades, the use of aluminum wheels on vehicles has become increasingly popular. This has led manufacturers to try to find more efficient, cost-effective methods of producing the wheels. The most common method of production involves casting an aluminum wheel into a near net shape and then machining the wheel until it meets the finished part specifications. The machining of aluminum wheels typically involves placing the wheel in a chuck, applying a clamping force with the chuck, and spinning the wheel at a relatively high speed while cutting tools are applied to the aluminum.
Before the mid-1980s, the chucks used to hold aluminum wheels typically applied the clamping force in a radial direction. Because a relatively high clamping force is required to hold a vehicle wheel, there is a tendency for an aluminum wheel to undergo a slight deformation when it is clamped in this type of chuck. A deformation of this kind reduces the accuracy with which the wheel can be machined. Specifically, this type of deformation may cause the wheel to have an undesirably large radial runout. In addition, the radial clamping chucks used to hold the wheels were quite large, which limited the speed at which the wheel could be spun. Because it is generally more efficient to machine aluminum alloys at high speeds, some efficiency was lost in the machining process because of the sheer bulk of the chucks used to clamp the wheels.
In the mid-1980s, an alternative to the large, radially clamping chucks was introduced. Generically known as a “pullback” chuck, the use of these chucks allowed for faster turning speeds and less distortion of the wheel resulting from clamping forces. A pullback chuck typically uses three equally spaced cam arms to apply the clamping force to a workpiece. The force is applied through the cam arms such that an initial radial force is redirected into a force that is parallel to the axis of rotation.
Pullback chucks often include a large diameter flat disk, or face plate, which is bolted to a smaller diameter shell, also known as a riser body. Corresponding to the three cam arms, the riser body has attached to it three yoked arms into which one end of each cam arm is pinned. A second pin, mounted within the face plate, provides a pivot point for the cam arms as the clamping force is applied. Mounted onto the face plate in the area outboard of the riser body are three equally spaced rest blocks. These blocks, or part rests, keep the wheel properly oriented during the machining operation.
The use of the pullback chuck allows aluminum wheels to be machined at higher speeds with less radial runout, thereby creating a superior finished product. Despite these advantages, the pullback chuck did introduce a minor distortion in the wheel in an axial direction, which often resulted in an undesirable lateral runout. As clamping forces sufficient to hold the wheel are applied, the face plate on a pullback chuck will often deflect slightly in the direction of the force. This deflection, which occurs around the perimeter of the face plate, may be in the neighborhood of 0.002-0.010 inches, and occurs almost uniformly at all three part rests. Aware of this unwanted deflection, manufacturers tended to rely on the offset capabilities of CNC lathe controllers to produce parts that met specifications. Recently, the demand for lighter, better riding vehicles has imposed upon wheel manufacturers increasingly tight tolerances. Today, controlling the deflection of the face plate in a pullback chuck can mean the difference between producing high quality finished parts that meet a customer's stringent specifications, or producing scrap.
Accordingly, it is desirable to provide anti-deflection tooling that is easily attached to an existing pullback chuck, and incorporated into the designs of new chucks, so that deflection of the workpiece is reduced or eliminated, thereby resulting in higher quality finished parts and a reduced scrap rate.